Power transmission



K. R. HERMAN 2,241,665

. POWER TRANSMISSION May 13, 1,941.

Filed Deq. 24, 1938 INVENTOR KENNETH R.HERMAN ATTORNEY Patented May 13,1941

rowEa TnANsMrssloN Kenneth R. Herman, Detroit. Mich., assigner to Vickers Incorporated, De

tion of Michigan troit, Mich., a corpor- 4Application December 24', 1938, Serial No. 247,577

s claims. (01. 10a-42) This invention relates to power transmissions.

particularly to those of the type comprising two or more fluid pressure energy translating devices one of which may function as a pump vand another as a uid motor. f l

The invention is particularly concerned with a power transmission system for use on aircraft for operating by power such movable parts asrequire too much eil'ort for manual actuation; such as wing flaps, retractable landing gear, brakes,

and indeed for operating any movable part which it may be desired to move. Due to space and weight limitations and to the intermittent use to which such a system is subjected, it is dsirable to provide a common pump for supplying uid pressure to operate the various fluid motors and transmission, system incorporating a preferred form of the present invention.

Figure 2 is a diagrammatic cross section ofthe unloading mechanism forming a part of the circuit illustrated in Figure 1.

J The hydraulic circuit includes a pump l0 having a suction conduit I2 for withdrawing oil from a tank I4 and delivering it to a delivery conduit 'I'he pump-I6 may be driven by a suitable prime mover such as an aircraft engine or the like. Delivery conduit I8 connects to a port I8 of an unloading valve 20. The pressure delivery to also provide an accumulator for not only permitting more rapid operation of a motor than character is that of providing suitable means for.

unloading the pump when the accumulator becomes filled so that power is not wasted in blowing oil overa relief valve at the full pressure developed in the accumulator. So far as applicant is aware, no unloading arrangement heretoforef would be otherwise permitted but also to form a reserve supply of oil under pressure capable of developed has proven entirely satisfactory for air craft service, among the difdculties beingl unreliability due to occasional failure of the unloading mechanism to reload the pump when demended by emptying of the accumulator, inability to shift from fully unloaded condition to fully loaded condition without requiring a very large drop in pressure at the accumulator. and large i weight and bulk.

Itis an object of the present invention to provide an improved power transmission system in which the above diiliculties are avoided and which in a simple compact light-weight mechanism provides positive unloading and reloading of the pump under the sole control of the accumulator pressure and which is effective on an extremely small pressure differential between unloading pressure and reloading pressure.

- The value 'i4 has a pressure port 16 which con- Further objects and advantages of the present I invention will be apparent from the following description, reference being had to the accomport 22 of the valve 20 isl connected by a conduit 24 with the pressure port of a four-way valve 26. A branch conduit 28 connects between the line 24 and an .air-loaded accumulator indicated diagrammaticaliy at 30. The cylinder ports of the valve 26 connect by conduits 82 and Si with the opposite sides of a fluid motor 36 for operating any desired load device.

The unloading valve 20 also has a bypass port 88 connected by a conduit 40 with the tank I4. A branch conduit 42 connects the tank port of valve 26 with the conduit 46.

The internal construction of the unloading valve is illustrated diagrammatically in Figure 2. `The port I8 connects by a conduit 44 with a check valve 46 the discharge side of which connects to the port 22. -A branch 48 leads from the conduit 44 to a port 6l)v of an unloading valve generally designated as 62. The latter has a port 64 communicating by a conduit 56 with the bypass port 88. The spool 6 8 in its position illustrated closes communication between ports 48 and 64, thus causing the entire delivery of the pump to pass over check valve 46 to port 22. With the spool 68 shifted to the left communication is opened from conduit 44 to conduit 66 thus permitting the pump delivery to be bypassed. The spool 68 is biased to the right by a light spring-60.

For controlling shifting of the spool 68 the end chambers of the bore 62 in which the spool slides are connected by conduits 64 and 66 with the cylj inder ports 'I0 and 12 of a four-way pilot valve Y generally designated as 14.

nects by a conduit 18 withthe conduit 44. A restrictor 86 is. preferably incorporated-in this connection and may comprise a plurality of apertured disks assembled between annular sepaspool 88 is arranged to be' shifted by pressure admitted toA the end chambers ot the bore 86 in' conduits 82 and 84 connect with the cylinder ports 96 and 88 of a four-way pilot valve |00 the pressure port |02 of which communicates with the conduit 44 by a branch connection |84.

Valve has a spool |06 having a hemispherical upper end provided with diametrically opposite flats |08 for passage of fluid .from the port 98 to the open end of the bore ||0 in which the spool |06 is slidable. A tank port ||2 and the space above the open end of bore ||8are connected to conduit 56 by a branch conduit ||4. The pilot valve |00 is arranged to operate as a pressure responsive valve by the. provision of a piston ||6 at the lower end-of the bore ||0 which is connected to the port 22 by a branch conduit I I8. The latter has a restrictor |20 therein. The

spool |06 `and piston ||6 are biased downwardly by a spring |20 resting on a spring plate |22 which seats on the hemispherical upper end of the spool |06. A spring housing |24 is secured' l to the top portion of the body of valve 20.

In operation, oil is withdrawn by the pump |'8 vfrom the tank |4 through the suction conduit i2 can occur. The unloading valve thus automati- V 3,241,665 I which the spool 88 is slidable. For this purpose end of bore 82 to balance the force of spring 88, no further movement of the spool 58 to the lett pressure from line 44 through connection |04,

ports |02 and 96, and conduit 82 to the righthand end of bore 90. The spool 88 accordingly shifts to the left' discharging oil from the left' end of bore through conduit 04, port 88, across- -the dats |08, and through conduit ||4-to tank;

. Shifting of the spool 88 admits pressure oil from by having moved the load to its extreme position,

oil will be delivered by the pump to the accumulator 30 filling the same until the pressure therein reaches a predetermined maximum. When this pressure is reached, the unloading valve 20 opens the bypass to port 88 and through conduit 40 to tank, thus bypassing the pump delivery while the check valve 46 prevents back ilow from the line 24 to tank. There is thus maintained a Isupply of oil under pressure in the accumulator 30 for eil'ecting rapid operation of the motor v26.

The showing of valve 20 in Figure 2 represents the position of the parts when the accumulator is not lled and the pump delivery is passing over the check valve 46 to the port 22. As soon as the maximum pressure is reached in the accumulator this pressure is transmitted through conduit ||8 and restrictor |20 to the piston ||6 which is -then ablev to overcome the force oi spring |28 ,nection 38. The shifting of pilot valve 14 admits pressure oil from conduit 44 through branch connectipn 18, ports 16 andA 10, and conduit 64 to the right-hand end of unloading Valve 52.

The spool 58 is accordingly shifted to the left against the bias of spring 60 until port 48 opens to-port 54. Oil discharged from the` left end of valve 52 .returns to tank through conduit 66, ports .12 and 84, conduits 86 and 56. As soon as unloading valve 52 cracks open, the pump delivery will be bypassed through connection 48, ports 80 and 54, and conduit 56 to'tank. 'Ihe spool 58 `cannot shift completely to the leit, however, be-

cause as soon as the port 50 is opened` so wide as to permit the pressure in line 44 to fall below the value that must be maintained in the right conduit," through connection 18, ports 'I6 and 12, and connection 68 to the left end of unloading valve 82. The valve is thenpositively. shifted to the right closing the bypass and discharging oil from the right 'end through conduit 64, porta 10 and 82, and conduit 86 to tank. The parts arev thus returned to the position shown on the drawing.

While the form of embodiment of the invention, as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a uid power transmission for driving an intermittently operating iiuid motor, thecombination of a continuously running pump, a supply connection from the pump to the motor, an accumulator in the supply connection, means bet n the pump and the accumulator for preven ing flow from the accumulator toward the ApuI11p.,|.'bypass 'between the pump and said said motor means, fluid motor means for shifting the pilot valve, a spring lloaded piston exposed to pressure in the supply line between said ilow preventing means and the iluid motor, and a pilot valve operated by the piston for controlling the second mentioned fluid motor means. y

2. In a iluid power transmission for driving an intermittently operating duid motor, the combination of a'continuously running pump, a supply connection from the pump to the motor, an accumulator in the supply connection, means between the pump and the accumulator for preventing iiow from the accumulator toward the pump, a bypass between the pump and said means, an unloading valve for opening and closing the bypass, fluid motor means for shifting the unloading valve in opposite directions, a pilot valve for controlling said motor means, iluid motor means for shifting the pilot valve, a spring pump, a bypass between the pump and said means, an unloading valve for opening and closing the bypass, nuid motor means for shifting the unloading valve, a pilot valve for controlling saidv motor means, `fluid motor means for shifting the pilot valve, a spring loaded piston exposed to pressure in the supply line between said flow' preventing means and the iluid motor, a pilot valve operated by the piston for controlling the second mentioned iluid motor means, anda restriction between the piston and the 'supply' line.

4. In a iluid power transmission'for driving an intermittently operating fluid motor, the combination of a continuously running pump, a supply connection from the pump to the motor, an accumulator in the supply connection; means between the pump and the accumulator for preventing flow from the accumulator toward the pump, a bypass between the pump and said means, an unloading valve for opening and clos- 'ing the bypass, fluid motor means-for shifting the unloading valve, a pilot valve for controlling said motor means, iiuid motor means for shifting the pilot Valve, a spring loaded piston lexposed to pressure in the supply line between said 1 now preventing, means and the uid motor, a

venting now from the accumulator toward the pump, a bypass between the pump and said means, an unloading valve for opening and closing the bypass, nuid motor means for shifting the unloading valve, a pilot valve for controlling said motor means, nuid motor means for shifting the pilot valve, means responsive to the prespilot valve operated by the piston for controllingthe second mentioned uid motor means, and connections for supplying fluid to operatel both said motor operated means from the supply line,

one of said connections being restricted and the other unrestricted.

5. In a uid power transmission for' driving an intermittently operating iiuid motor, the combination of a continuously running pump, val

supply connection from the pump to the motor,

an accumulator in the supply connection, means ,l

between the pump and the accumulator for pre-l venting ow from the. accumulator toward the pump, a bypass between the pump and said means, `an unloading valve for opening and closing the bypass, iluid motor means for shifting the unloading valve, a pilotvalve for controlling said motor means, fluid motor means for shifting the pilot valve, means responsive to the pressure in the supply line between said flow preventing means and the accumulator for controlling the pilot valve, a connection for supplying fluid tooperate the unloading valve from the supply line between the pump and the bypass, and means for Amaintaining a small pressure in said connection during unloading of the pump.

6. In a uid power transmission for ldriving an intermittently operating. iluid motor, the combination of a-continuously runningl pump, a supply connection from the pump to the motor. an accumulator in the supply connection, means between the pump and the accumulator for presure in the supply line between said iiow preventing means and the accumulator for controlling the pilot valve, and a connection for supply.= ing fluid to operate the unloading valve from the supply line between the pump and the bypass, said unloading valve being biased to maintain a small pressure in said connectionduring unloading of the pump.

7. In a fluid power transmission for driving an intermittently operating iluid motor, the combination of a continuously running pump, a supply connection from the pump to the motor, an accumulator in the supply connection, means between the pump andthe accumulator for preventing ow from the accumulator toward the pump, a bypass between the pump and said means, an unloading valve for opening and closing thel bypass, a. pressure responsive element connected with the accumulator and responsive t9 pressure changes therein, and means controlled by said pressure responsive element for governing the rate of change of opening or closing movement of the unloading valve, said means Aoperating on a predeterminedV increase in accumulator pressure to impart a predetermined opening acceleration to the unloading valve and upon a predetermined decrease to impart a p redetermined closing acceleration thereto.

8. In a nuidpower transmission, for driving an intermittently operating uid motor, vthe combination of a continuously running pump, a supply connection from the pump to the motor, an accumulator inthe supply connection. means between thel pump and the accumulator for pre-` Y venting now from the accumulator toward the pump,` a bypass betweemthe pump andsaid 4 means, an unloading valve for opening and closing the bypass,

a pressure responsive element connected with the accumulator and responsive to pressure changes therein, means controlled by said pressure vresponsive element' for governing the rate of changeoi opening or closing movement of the unloading valve, said means operating on a predetermined increase in accumulator pressureto impart a predetermined opening ac-y celera-tion to the unloading valve and upon a predetermined decrease to impart a predeterl mined closing acceleration thereto, and means vyieldably Abiasing said unloading valve toward closed position at all times.

KENNETH R. HERMAN. 

